[RFC PATCH 4/7] dma: swiotlb: track pool encryption state and honor DMA_ATTR_CC_DECRYPTED

Aneesh Kumar K.V (Arm)
2026-04-17T09:00:01Z

Teach swiotlb to distinguish between encrypted and decrypted bounce
buffer pools, and make allocation and mapping paths select a pool whose
state matches the requested DMA attributes.

Add a decrypted flag to io_tlb_mem, initialize it for the default and
restricted pools, and propagate DMA_ATTR_CC_DECRYPTED into swiotlb pool
allocation. Reject swiotlb alloc/map requests when the selected pool does
not match the required encrypted/decrypted state.

Also return DMA addresses with the matching phys_to_dma_{encrypted,
unencrypted} helper so the DMA address encoding stays consistent with the
chosen pool.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
include/linux/dma-direct.h | 10 +++++
include/linux/swiotlb.h | 7 ++-
kernel/dma/direct.c | 14 ++++--
kernel/dma/swiotlb.c | 89 ++++++++++++++++++++++++++++++--------
4 files changed, 95 insertions(+), 25 deletions(-)

diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
index c249912456f9..94fad4e7c11e 100644
--- a/include/linux/dma-direct.h
+++ b/include/linux/dma-direct.h
@@ -77,6 +77,10 @@ static inline dma_addr_t dma_range_map_max(const struct bus_dma_region *map)
#ifndef phys_to_dma_unencrypted
#define phys_to_dma_unencrypted phys_to_dma
#endif
+
+#ifndef phys_to_dma_encrypted
+#define phys_to_dma_encrypted phys_to_dma
+#endif
#else
static inline dma_addr_t __phys_to_dma(struct device *dev, phys_addr_t paddr)
{
@@ -90,6 +94,12 @@ static inline dma_addr_t phys_to_dma_unencrypted(struct device *dev,
{
return dma_addr_unencrypted(__phys_to_dma(dev, paddr));
}
+
+static inline dma_addr_t phys_to_dma_encrypted(struct device *dev,
+ phys_addr_t paddr)
+{
+ return dma_addr_encrypted(__phys_to_dma(dev, paddr));
+}
/*
* If memory encryption is supported, phys_to_dma will set the memory encryption
* bit in the DMA address, and dma_to_phys will clear it.
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 3dae0f592063..382753ba3f06 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -111,6 +111,7 @@ struct io_tlb_mem {
struct dentry *debugfs;
bool force_bounce;
bool for_alloc;
+ bool decrypted;
#ifdef CONFIG_SWIOTLB_DYNAMIC
bool can_grow;
u64 phys_limit;
@@ -282,7 +283,8 @@ static inline void swiotlb_sync_single_for_cpu(struct device *dev,
extern void swiotlb_print_info(void);

#ifdef CONFIG_DMA_RESTRICTED_POOL
-struct page *swiotlb_alloc(struct device *dev, size_t size);
+struct page *swiotlb_alloc(struct device *dev, size_t size,
+ unsigned long attrs);
bool swiotlb_free(struct device *dev, struct page *page, size_t size);

static inline bool is_swiotlb_for_alloc(struct device *dev)
@@ -290,7 +292,8 @@ static inline bool is_swiotlb_for_alloc(struct device *dev)
return dev->dma_io_tlb_mem->for_alloc;
}
#else
-static inline struct page *swiotlb_alloc(struct device *dev, size_t size)
+static inline struct page *swiotlb_alloc(struct device *dev, size_t size,
+ unsigned long attrs)
{
return NULL;
}
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index ba1c731e001d..4a4147fffc5e 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -104,9 +104,10 @@ static void __dma_direct_free_pages(struct device *dev, struct page *page,
dma_free_contiguous(dev, page, size);
}

-static struct page *dma_direct_alloc_swiotlb(struct device *dev, size_t size)
+static struct page *dma_direct_alloc_swiotlb(struct device *dev, size_t size,
+ unsigned long attrs)
{
- struct page *page = swiotlb_alloc(dev, size);
+ struct page *page = swiotlb_alloc(dev, size, attrs);

if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
swiotlb_free(dev, page, size);
@@ -256,8 +257,12 @@ void *dma_direct_alloc(struct device *dev, size_t size,
gfp, attrs);

if (is_swiotlb_for_alloc(dev)) {
- page = dma_direct_alloc_swiotlb(dev, size);
+ page = dma_direct_alloc_swiotlb(dev, size, attrs);
if (page) {
+ /*
+ * swiotlb allocations comes from pool already marked
+ * decrypted
+ */
mark_mem_decrypt = false;
goto setup_page;
}
@@ -364,6 +369,7 @@ void dma_direct_free(struct device *dev, size_t size,
return;

if (swiotlb_find_pool(dev, dma_to_phys(dev, dma_addr)))
+ /* Swiotlb doesn't need a page attribute update on free */
mark_mem_encrypted = false;

if (is_vmalloc_addr(cpu_addr)) {
@@ -393,7 +399,7 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
gfp, attrs);

if (is_swiotlb_for_alloc(dev)) {
- page = dma_direct_alloc_swiotlb(dev, size);
+ page = dma_direct_alloc_swiotlb(dev, size, attrs);
if (!page)
return NULL;

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 2373a9f7e21a..1b845596b68f 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -262,7 +262,18 @@ void __init swiotlb_update_mem_attributes(void)
if (!mem->nslabs || mem->late_alloc)
return;
bytes = PAGE_ALIGN(mem->nslabs << IO_TLB_SHIFT);
- set_memory_decrypted((unsigned long)mem->vaddr, bytes >> PAGE_SHIFT);
+ /*
+ * if platform support memory encryption, swiotlb buffers are
+ * decrypted by default.
+ */
+ if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
+ io_tlb_default_mem.decrypted = true;
+ set_memory_decrypted((unsigned long)mem->vaddr, bytes >> PAGE_SHIFT);
+ } else {
+ io_tlb_default_mem.decrypted = false;
+ }
+
+
}

static void swiotlb_init_io_tlb_pool(struct io_tlb_pool *mem, phys_addr_t start,
@@ -505,8 +516,10 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask,
if (!mem->slots)
goto error_slots;

- set_memory_decrypted((unsigned long)vstart,
- (nslabs << IO_TLB_SHIFT) >> PAGE_SHIFT);
+ if (io_tlb_default_mem.decrypted)
+ set_memory_decrypted((unsigned long)vstart,
+ (nslabs << IO_TLB_SHIFT) >> PAGE_SHIFT);
+
swiotlb_init_io_tlb_pool(mem, virt_to_phys(vstart), nslabs, true,
nareas);
add_mem_pool(&io_tlb_default_mem, mem);
@@ -570,7 +583,8 @@ void __init swiotlb_exit(void)
* Return: Decrypted pages, %NULL on allocation failure, or ERR_PTR(-EAGAIN)
* if the allocated physical address was above @phys_limit.
*/
-static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes, u64 phys_limit)
+static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes,
+ u64 phys_limit, bool unencrypted)
{
unsigned int order = get_order(bytes);
struct page *page;
@@ -588,13 +602,13 @@ static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes, u64 phys_limit)
}

vaddr = phys_to_virt(paddr);
- if (set_memory_decrypted((unsigned long)vaddr, PFN_UP(bytes)))
+ if (unencrypted && set_memory_decrypted((unsigned long)vaddr, PFN_UP(bytes)))
goto error;
return page;

error:
/* Intentional leak if pages cannot be encrypted again. */
- if (!set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
+ if (unencrypted && !set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
__free_pages(page, order);
return NULL;
}
@@ -604,12 +618,13 @@ static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes, u64 phys_limit)
* @dev: Device for which a memory pool is allocated.
* @bytes: Size of the buffer.
* @phys_limit: Maximum allowed physical address of the buffer.
+ * @attrs: DMA attributes for the allocation.
* @gfp: GFP flags for the allocation.
*
* Return: Allocated pages, or %NULL on allocation failure.
*/
static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,
- u64 phys_limit, gfp_t gfp)
+ u64 phys_limit, unsigned long attrs, gfp_t gfp)
{
struct page *page;

@@ -617,7 +632,7 @@ static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,
* Allocate from the atomic pools if memory is encrypted and
* the allocation is atomic, because decrypting may block.
*/
- if (!gfpflags_allow_blocking(gfp) && dev && force_dma_unencrypted(dev)) {
+ if (!gfpflags_allow_blocking(gfp) && (attrs & DMA_ATTR_CC_DECRYPTED)) {
void *vaddr;

if (!IS_ENABLED(CONFIG_DMA_COHERENT_POOL))
@@ -625,8 +640,7 @@ static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,

/* considered decrypted by default */
return dma_alloc_from_pool(dev, bytes, &vaddr, gfp,
- DMA_ATTR_CC_DECRYPTED,
- dma_coherent_ok);
+ attrs, dma_coherent_ok);
}

gfp &= ~GFP_ZONEMASK;
@@ -635,7 +649,8 @@ static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,
else if (phys_limit <= DMA_BIT_MASK(32))
gfp |= __GFP_DMA32;

- while (IS_ERR(page = alloc_dma_pages(gfp, bytes, phys_limit))) {
+ while (IS_ERR(page = alloc_dma_pages(gfp, bytes, phys_limit,
+ !!(attrs & DMA_ATTR_CC_DECRYPTED)))) {
if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
phys_limit < DMA_BIT_MASK(64) &&
!(gfp & (__GFP_DMA32 | __GFP_DMA)))
@@ -673,6 +688,7 @@ static void swiotlb_free_tlb(void *vaddr, size_t bytes)
* @nslabs: Desired (maximum) number of slabs.
* @nareas: Number of areas.
* @phys_limit: Maximum DMA buffer physical address.
+ * @attrs: DMA attributes for the allocation.
* @gfp: GFP flags for the allocations.
*
* Allocate and initialize a new IO TLB memory pool. The actual number of
@@ -683,7 +699,8 @@ static void swiotlb_free_tlb(void *vaddr, size_t bytes)
*/
static struct io_tlb_pool *swiotlb_alloc_pool(struct device *dev,
unsigned long minslabs, unsigned long nslabs,
- unsigned int nareas, u64 phys_limit, gfp_t gfp)
+ unsigned int nareas, u64 phys_limit, unsigned long attrs,
+ gfp_t gfp)
{
struct io_tlb_pool *pool;
unsigned int slot_order;
@@ -703,7 +720,7 @@ static struct io_tlb_pool *swiotlb_alloc_pool(struct device *dev,
pool->areas = (void *)pool + sizeof(*pool);

tlb_size = nslabs << IO_TLB_SHIFT;
- while (!(tlb = swiotlb_alloc_tlb(dev, tlb_size, phys_limit, gfp))) {
+ while (!(tlb = swiotlb_alloc_tlb(dev, tlb_size, phys_limit, attrs, gfp))) {
if (nslabs <= minslabs)
goto error_tlb;
nslabs = ALIGN(nslabs >> 1, IO_TLB_SEGSIZE);
@@ -739,7 +756,9 @@ static void swiotlb_dyn_alloc(struct work_struct *work)
struct io_tlb_pool *pool;

pool = swiotlb_alloc_pool(NULL, IO_TLB_MIN_SLABS, default_nslabs,
- default_nareas, mem->phys_limit, GFP_KERNEL);
+ default_nareas, mem->phys_limit,
+ mem->decrypted ? DMA_ATTR_CC_DECRYPTED : 0,
+ GFP_KERNEL);
if (!pool) {
pr_warn_ratelimited("Failed to allocate new pool");
return;
@@ -1226,6 +1245,7 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
nslabs = nr_slots(alloc_size);
phys_limit = min_not_zero(*dev->dma_mask, dev->bus_dma_limit);
pool = swiotlb_alloc_pool(dev, nslabs, nslabs, 1, phys_limit,
+ mem->decrypted ? DMA_ATTR_CC_DECRYPTED : 0,
GFP_NOWAIT);
if (!pool)
return -1;
@@ -1388,6 +1408,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
enum dma_data_direction dir, unsigned long attrs)
{
struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
+ bool require_decrypted = false;
unsigned int offset;
struct io_tlb_pool *pool;
unsigned int i;
@@ -1405,6 +1426,17 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
pr_warn_once("Memory encryption is active and system is using DMA bounce buffers\n");

+ /*
+ * if we are trying to swiotlb map a decrypted paddr or the paddr is encrypted
+ * but the device is forcing decryption, use decrypted io_tlb_mem
+ */
+ if ((attrs & DMA_ATTR_CC_DECRYPTED) ||
+ (!(attrs & DMA_ATTR_CC_DECRYPTED) && force_dma_unencrypted(dev)))
+ require_decrypted = true;
+
+ if (require_decrypted != mem->decrypted)
+ return (phys_addr_t)DMA_MAPPING_ERROR;
+
/*
* The default swiotlb memory pool is allocated with PAGE_SIZE
* alignment. If a mapping is requested with larger alignment,
@@ -1602,8 +1634,14 @@ dma_addr_t swiotlb_map(struct device *dev, phys_addr_t paddr, size_t size,
if (swiotlb_addr == (phys_addr_t)DMA_MAPPING_ERROR)
return DMA_MAPPING_ERROR;

- /* Ensure that the address returned is DMA'ble */
- dma_addr = phys_to_dma_unencrypted(dev, swiotlb_addr);
+ /*
+ * Use the allocated io_tlb_mem encryption type to determine dma addr.
+ */
+ if (dev->dma_io_tlb_mem->decrypted)
+ dma_addr = phys_to_dma_unencrypted(dev, swiotlb_addr);
+ else
+ dma_addr = phys_to_dma_encrypted(dev, swiotlb_addr);
+
if (unlikely(!dma_capable(dev, dma_addr, size, true))) {
__swiotlb_tbl_unmap_single(dev, swiotlb_addr, size, dir,
attrs | DMA_ATTR_SKIP_CPU_SYNC,
@@ -1765,7 +1803,8 @@ static inline void swiotlb_create_debugfs_files(struct io_tlb_mem *mem,

#ifdef CONFIG_DMA_RESTRICTED_POOL

-struct page *swiotlb_alloc(struct device *dev, size_t size)
+struct page *swiotlb_alloc(struct device *dev, size_t size,
+ unsigned long attrs)
{
struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
struct io_tlb_pool *pool;
@@ -1776,6 +1815,9 @@ struct page *swiotlb_alloc(struct device *dev, size_t size)
if (!mem)
return NULL;

+ if (mem->decrypted != !!(attrs & DMA_ATTR_CC_DECRYPTED))
+ return NULL;
+
align = (1 << (get_order(size) + PAGE_SHIFT)) - 1;
index = swiotlb_find_slots(dev, 0, size, align, &pool);
if (index == -1)
@@ -1845,9 +1887,18 @@ static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
kfree(mem);
return -ENOMEM;
}
+ /*
+ * if platform supports memory encryption,
+ * restricted mem pool is decrypted by default
+ */
+ if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
+ mem->decrypted = true;
+ set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
+ rmem->size >> PAGE_SHIFT);
+ } else {
+ mem->decrypted = false;
+ }

- set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
- rmem->size >> PAGE_SHIFT);
swiotlb_init_io_tlb_pool(pool, rmem->base, nslabs,
false, nareas);
mem->force_bounce = true;
--
2.43.0